The volume of a unit of blood is approximately 1 pint (450–500 mL). Units of blood collected from donors are separated into multiple components, such as packed red blood cells, platelets, and plasma. Red blood cells may be stored for a maximum of 42 days. Older blood is less effective. It has been clear for some time that stored blood degrades before the 42-day limit, and some research suggests that this degradation may be harmful to patients who receive older blood. In fact, 75% of red blood cells should survive post-transfusion to be classified as a successful transfusion.
There are three areas of concern during the preservation and storage of red blood cells:
Red blood cell metabolism—The function of red blood cells is to transport oxygen. However, erythrocytes do not have mitochondria, which is the site of aerobic respiration. Instead, red blood cells produce ATP anaerobically by the breakdown of glucose, thus not using any of the oxygen for their own metabolism. Anaerobic metabolism allows red blood cells to deliver 100% of the oxygen to the organ sites.
Red blood cell membrane function—A recent study has shown that increased duration of erythrocyte storage is associated with decreased cell membrane deformability. Furthermore, these changes are not readily reversible after transfusion. The decreased deformability is the result of damage over time. Changes in red blood cell morphology occurred as quickly as 22 days. This alteration can be harmful because red blood cells are similar in size to the diameter of small capillaries; therefore, red blood cells have to change shape to get through the capillaries.
Hemoglobin function—2,3-diphosphoglycerate (DPG) is a carbon molecule important in erythrocyte metabolism. It binds to deoxygenated hemoglobin and increases oxygen off-loading from hemoglobin into the tissues. As erythrocyte storage time increases, the levels of 2,3-DPG decrease. Transfusion of 2,3-DPG-depleted blood may shift the oxygen–hemoglobin dissociation curve to the left. As a result, red blood cells will have difficulty in unloading oxygen from hemoglobin into the issues.
Citrate–phosphate–dextrose (CPD), an anticoagulant solution, is the mainstay of blood preservation. Citrate works as an anticoagulant by binding to and inhibiting the function of calcium (factor IV). Phosphate stabilizes pH which maintains proper levels of 2,3-DPG. The dextrose component is necessary for red blood cell ATP production. If adenine, a purine nucleotide, is added to CPD (CPD-A), storage time jumps from 21 days to 35 days. Adenine assists in the production of ATP.
Red Blood Cell Additive Solutions
Additive solutions replace nutrients lost when the plasma is removed from red blood cells. When additive solutions are added, red blood cell’s storage time can be increased from 35 days to 42 days. Two of the solutions (Adsol, Optisol) contain adenine, glucose, saline, and mannitol. Mannitol prevents hemolysis in the stored red ...